1. Field of the Invention
The present invention relates to a suspension device including: a knuckle formed by a knuckle body and a lower arm support bracket fastened to front and rear fastening portions provided in a lower portion of the knuckle body with front and rear bolts; and a lower arm having an inner end portion in a vehicle width direction connected to a vehicle body, and an outer end portion in the vehicle width direction connected to the lower arm support bracket.
2. Description of the Related Art
FIGS. 7 and 8 show a conventional suspension device. A knuckle 01 of the suspension device is formed by connecting a lower arm support bracket 03 to a lower end of a knuckle body 02 with two bolts 04 and 05. An outer end of an upper arm 06 in a vehicle width direction is connected to an upper end of the knuckle 01 via a ball joint 08. An outer end of a lower arm 07 in the vehicle width direction is connected to the lower arm support bracket 03 via a ball joint 09. A pair of fastening portions 02a and 02b protruding downward are integrally formed at front and rear ends in a lower portion of the knuckle body 02. Front and rear ends of the lower arm support bracket 03 are fastened to fastening surfaces of the fastening portions 02a and 02b with the bolts 04 and 05.
When a vehicle turns at high speed, a vehicle body leans outward in a turning direction by centrifugal force caused by the turning and a turning outside wheel thus bumps, and a turning lateral force acting inward in the turning direction is applied to a ground contact point of the turning outside wheel. As shown in FIG. 8, in the knuckle 01 of the conventional suspension device, a line L connecting the fastening surfaces of the front and rear fastening portions 02a and 02b at which the lower arm support bracket 03 is fastened to the knuckle body 02, is inclined downward to the front in a normal state (under acceleration of 1 G in a vertical direction). When a wheel bumps, the line L is further inclined downward to the front and moves to a position L′. This increases a difference in height from a road surface to the front and rear bolts 04 and 05, and when the lateral force is applied, a load applied to the rear bolt 05 becomes larger than a load applied to the front bolt 04 for reasons described in embodiments. Thus, when front and rear bolts 04 and 05 having the same diameter are used, durability of the rear bolt 05 to which a larger load is applied may be reduced.
In the above described conventional suspension device, when no load F toward a rear of a vehicle body is applied to a wheel W, a line A connecting the two bolts 04 and 05 fastening the lower arm support bracket 03 to the lower end of the knuckle body 02 is aligned with a front-rear direction of the vehicle body. Thus, when the wheel W passes over an uneven spot on the road surface or a brake is applied to the wheel W to cause the load F toward the rear of the vehicle body to act on the knuckle 01, the line A tends to toe-out to a position A′ together with the wheel W.
As a result, the front bolt 04 is displaced outward in the vehicle width direction from the line A running along the front-rear direction of the vehicle body, and the rear bolt 05 is displaced inward in the vehicle width direction from the line A along the front-rear direction of the vehicle body, and thus the load F causes a significant moment with the displacement as moment arms to act on the fastening portions 02a and 02b of the knuckle body 02. This problem requires some countermeasures such as increasing thicknesses of the front and rear bolts 04 and 05, thereby increasing weights.